The objective of this Phase I proposal is to demonstrate that cultured human colon tumor cell lines produce auto-inhibitory factors. In addition, the molecular weight of the inhibitory factor will be determined. Conditioned media will be collected from the SW-480 cell line under both serum-containing and serum-free conditions. The fractionation procedures have been designed to effectively identify both possible high molecular weight and low molecular weight inhibitory factors. The specificity of the inhibitor will be determined by in vitro assays with a wide variety of normal and tumor cell lines. The successful completion of Phase I will provide the data necessary for further development of auto-inhibitory factors for human colon tumors. The molecular weight determined during Phase I will be used to design the necessary protocols for complete purification of the inhibitory factor and its eventual large scale production. This production will be through eigher gene-cloning if the inhibitor is of high molecular weight or by chemical synthesis if the inhibitor is low molecular weight. The successful development of such an inhibitor, specific for colon tumors, would be of great usefulness in the treatment of colon cancer, one of the predominant human cancers.